The present invention concerns glass-ceramic cooktops and/or cooking ranges with radiating heating elements.
Glass-ceramic cooking ranges with radiating heating elements are already known. They are low priced and they have stood the test for years a million times over. These radiating heating elements are quite sluggish in the first minutes of warm-up. As a result of the type and design of the insulation material, and because of the type and fixation of the heating conductor (heating wire or filament), the bulk of the heating conductor and the immediately adjacent mass of insulation has to be heated up initially after the switching on of current to the heating conductor. This leads to the situation that in the first seconds after switching on the heating element, the heating conductor or coil does not glow and thus are not visible, even through a sufficiently translucent glass-ceramic cooking surface. This lack of visibility is considered to be a great disadvantage.
On the other hand, the quick visibility of the switched on heating conductor is greatly desired by the housewife, in order to be able to perceive quickly the on-condition of the heating conductor, especially to be able to perceive immediately when the heating element has been switched on mistakenly. At least for this reason, heating elements for glass-ceramic cooking ranges have been developed with halogen lamps, where the halogen lamp lights up brightly immediately following the switching on of current to the corresponding heating conductor. The big disadvantage of these halogen lamps, and the manufactured heating elements employing such lamps is that they are very expensive and that special heating element geometries or designs are not possible because of the rod-shaped halogen lamps.
The goal of the present invention is a glass-ceramic cooking range, which is so constructed, and whose heating elements are electrically so configured, that the disadvantageous sluggishness of the radiating heating element during the warm-up phase is circumvented, whereby the high costs of heating elements with halogen lamps are avoided and simultaneously the hitherto diversity of heating element geometries and designs can be retained. This goal is achieved with a cooking range having cooking surfaces made of glass-ceramic or comparable material, with radiating heating elements with at least two heating circuits and with suitably related control elements. The heating circuit in the radiating heating element is so designed, or, the heating conductors of the radiating heating element are so wired and/or are connected by such circuitry and that a suitable switch element is connected to the heating circuits, that in the first heating-up phase, one or more heat conductors are in a short time so overloadable--referring to its rated power output--that in less than 20 seconds, and preferably in less than 5 seconds, it starts to glow and thus, through the sufficiently transparent cooking surface, becomes luminous. Through the suitably connected switch element, after a preselected time and/or after a preselected temperature of the heating conductor is reached, the heating output (wattage) of one or more of the heating circuits can, by one or more grades, be reduced to a lower output in such a way, that during the continuous operation of the radiating heating element following the heat-up phase, an overloading of the heating conductor is avoided.
An advantageous arrangement of a cooking range according to the present invention provides for an external switch, heated by the heating conductor current, instead of or in addition to the main switch element. For example, several heating circuits can be arranged within the radiating heating elements, which together or partially during the heat-up phase are driven in parallel connection and which through the switch element, after a preselected time or after reaching a preselected temperature are totally or partially switched over to a series connection and thus to a reduced output. The switch element can be a heated bi-metal switch which is heated by the heating conductor current, and through which occurs in accordance with its preselected switching characteristic, the switching from parallel to series connection. Alternatively, a bi-metal switch can be placed in or on the radiating heating element, the switch being heat activated through the warming of the heating element or heat conductor and thus, according to a preselected switching characteristic, effects the switching from parallel to series connection.
In another advantageous arrangement of a cooking range according to the present invention, a series resistance with a positive temperature coefficient is connected in series as a switch element of one or more heating circuits, which initially allows a high current, but with increasing warmth decreases the current and thereby the glowing of the heating conductors by increased resistance. In this arrangement of the cooking range, the heating circuit can be fitted with appropriate matching series resistance in the outer area of the heating element.
In yet another arrangement of a cooking range according to the present invention, a time driven or controlled unit is used as a switching element, which after the passing of a preselected time period effects a reduction in heating output by means of suitably devised switch elements. In each of the possible arrangements, suitable wiring of the heating conductor and/or use of suitable control elements results in the switching to the highest output level results only during the initial heat-up phase after the switching on of the control element.
The invention can be universally realized with all types of radiating heating elements, whether single-circuit or multi-circuit heating elements, and can be combined with common control elements of radiating heating elements. The costs of such solutions are meaningfully cheaper than those of heating elements with halogen lamps. After switching on these heating elements, the heating conductors glow within seconds and are visible through the cooking surface. At the same time, immediately after switching on, one can feel the heat generated through the glowing heat conductor above the cooking surface, which strengthens the impression of a lightning-speed heating.